Non-magnetic copper base alloys



United States Patent Ofifice 3,224,875 Patented Dec. 21, 1965 3,224,875 NON-MAGNETIC COPPER BASE ALLOYS William .l. Buehler, Adelphi, and Raymond C. Wiley,

Rocltville, Md., assignors to the United States of America as represented by the Secretary of the Navy No Drawing. Filed July 30, 1963, Ser. No. 298,796

6 Claims. C1. 75ll53) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to novel, hardenable, copperbase alloys suitable for use as non-magnetic tools and, in particular, to novel, non-magnetic copper-base alloys containing small quantities of silicon, magnesium or a combination of silicon and magnesium.

serviceable tools such as, for example, pliers, screwdrivers, hammers and wrenches that are initially nonmagnetic and which will remain non-magnetic throughout their useful life are of considerable interest to the United States Government for use in working on magnetic-sensitive explosive devices. In order to replace the iron base tools, which are highly ferromagnetic, it is required that the nonmagnetic replacement material be capable of being worked and machined to the desired final shape while in a softened condition and that these shaped tools then be capable of being hardened, and possiby tempered, by some reasonable heat treating schedule. The resultant tools should then possess sufficient high hardness, toughness, strength, particularly yield strength, elastic modulus, and abrasion resistance to be continuously useable, reliable and etlicient.

The art has, in general, encountered great difiiculties in developing non-magnetic materials capable of supplying the required mechanical properties. Since there is a direct relationship between hardness and tensile strength, a first measure of the suitability of a material is the degree of hardness to which it is amenable. Iron-base tools, particularly the deep hardened steels, are generally capable of hardening through to a value in excess of 60 R These hardened steels may then be tempered to lower the hardness to any desired level. The lowering of this hardness is associated with an increase in toughness which accompanies the tempering treatment. As a consequence, hardness values similar to those capable of being obtained in hardened steel are sought in non-magnetic tool materials. if the required high hardness, strength and toughness are obtained in a non-magnetic material, then it follows that the resulting tools produced from these materials should perform similar to the steel tools in all respects and, in addition, will remain nonmagnetic throughout their useful life.

in the past, various precipitation hardening copperbase alloys have been tried, including beryllium-copper, silicon bronzes, manganese bronzes, and Cu-Ni-Mn ternary alloys. Much interest has been directed lately to the latter compositions referred to commercially as Type 720 and Type 730. The 720 alloy consists of Ni, 20% Mn and 60% Cu. The 730 alloy contains Ni, 30% Mn and Cu. The alloys of this general type are known to be nonmagnetic in all conditions of heat treatment. Generally elements present in these alloys, other than nickel, copper and manganese, are present as impurities. In certain instances however, small percentages of other elements such as iron, carbon, silicon, aluminum and silver have been added to basic alloys in order to modify the properties thereof. It is generally recognized however, that the introduction of such additives must be carefully regulated in order to evade the objectionable properties introduced by adding too little or too great a quantity of such additive.

The presence of even small amounts of silicon has, in fact, been held to be markedly detrimental on alloys in which manganese is employed in relatively large quantities. Such alloys have been characterized as. having very poor working properties and as being extremely brittle when formed to shape by any method. With reference to the Type 720 and Type 730 alloys, it is generally conceded that the best results, in regard to the entire range of properties, are obtainable when the system contains only copper, manganese and nickel. So far as the Type 720 and Type 730 alloys are concerned, additives in more than very small quantities are considered objectionable, particularly in regard to the adverse effects on the range of hardness and tensile strength. It has also been recognized that the ductility of the Cu-Ni-Mn alloys is affected by the use of less than extremely high purity manganese.

Although the 720 and 730 alloys are very useful industrial compositions, they do have certain disadvantages. For example, those alloys having rather high nickel and manganese percentages (for example, approximately 30%) require a very narrow hot working temperature range which, if exceeded, contributes to alloy failure due to hot shortness. Moreover, the maximum hardness possible in the 720 alloy is too low for many tool applications and the 730 alloy (30% Ni, 30% Mn), although capable of being hardened sutficiently, is quite brittle and lacks the required toughness. Note, for example, Table l for hardness comparisons.

TABLE I Max. hardness (Rockwell) Nominal alloy after solution and aging compositions: (400 C.) treatments, R

20 Ni-ZO MnCu 37 22 Ni22 Mn-Cu 39 25 Ni25 MnCu 47 30 Ni-30 MnCu 49 Now, since the 720 alloy fails to meet the required hardness for many tool applications, higher nickel contents are necessary to produce useful compositions. Since, however, copper is cheaper and more readily available than nickel, it is desirable to confine the alloy composition to the minimum nickel and maximum copper concentrations commensurate with the desired end properties.

in spite of the difficulties of the prior art in obtaining Cu-NiMn ternary alloys having the required properties to produce serviceable tools, applicants have unexpectedly and surprisingly found that the addition of small quantitles of silicon and/or magnesium greatly improves the toughness of the Cu-Ni-Mn alloys in spite of the contraindicated teachings of the art.

Again, with reference to Table I, it may be seen that a 20 Ni-20 Mn-Cu alloy is only capable of a maximum hardness of 37 R while by increasing the Ni and Mn to 30 Ni-30 Mn-Cu the maximum hardness is increased to 49 R However, when the Ni and Mn are increased to 30 weight percent each, the toughness and impact resistance of the alloy sutfers badly.

In view of the problems of the prior art, it is an object of this invention to provide Cu-Ni-Mn alloys containing relatively low NiMn concentrations having heat treated hardnesses which approach or exceed the value of 50 R By increasing this heat treated hardness, the associated disadvantages of having to employ high Ni and Mn concentartions to get high hardness is eliminated. Moreover, the need for excessive quantities of Ni and Mn to produce a required hardness effect is eliminated by the minor addition of inexpensive, nonstrategic metallic elements.

A further object of this invention is to provide a treating process for Cu-Ni-Mn alloys which will promote miximum hardness properties within a reasonable time period.

The theory behind the hardenable Cu-Ni-Mn alloys is that a stable second phase of MnNi precipitates from solid solution and thereby increases the hardness. Applicants have discovered that the initial precipitation hardening mechanism of the MnNi phase may be supplemented by the addition of silicon and/or magnesium in order to produce precipitation of additional stable intermetallic compositions such as, for example, Ni Si Mn Si Mg Ni The novel alloys of this invention contain from about 19 to about 25 wt. percent nickel and from about 19 to about 25 wt. percent manganese having incorporated therein up to about 1.5 wt. percent silicon or up to about 1.0 wt. percent magnesium or up to about 2.0 wt. percent of a mixture of silicon and magnesium in a ratio of about 1 to 1 to 2 to 1 with the remainder being copper. The preferred alloy compositions contain from about 22 to about 24 wt. percent nickel, from about 22 to 24 wt. perd aging temperature used. Temperatures lower in this range require longer time to produce maximum hardness but, in most cases, yield the highest final hardness.

Employing the alloy compositions as set forth above, a series of tests were run to determine the effects of varying the silicon, magnesium and silicon plus magnesium additions on the hardening properties of the alloys. Tests were also run to show the effects of cold rolling, between the solution and againg heat treatments, upon the maximum obtainabie hardness of the alloys.

Table II shows the effects of varying silicon, magnesium and silicon plus magnesium additions upon the hardening properties of a nominal 22% nickel, 22% manganese, copper alloy. It is seen that optimum hardness for silicon additions (46 R occurs at additions up to about 1.2 percent. Higher silicon additions only lower the final maximum hardness. A similar effect is seen in the 0.5 percent magnesium addition. Higher amounts of magnesium lower the maximum obtainable hardness. Combinations of silicon and magnesium yield higher hardnesses when added in an amount up to about 2.0 percent by weight.

TABLE II.-PRECIPITATION HARDENING DATA FOR I-IOT ROLLED NOMINAL 22% N1, 22% M11, Cu ALLOYS WITII Si, Mg, AND

Si+Mg ADDED Nominal charge composition Solution Solution Aging Total aging time, hours As rolled treatment treatment tempora- No. hardness temporahardness turo, C.

Cu Ni Mn Si Mg ture, C.* 2 5 10 6O 90 55. 6 21.95 21.95 635 400 86 RB 29 Re 36 R0 41 Re 46 R0 46 Be 55.4 21. 75 21.75 635 400 91 R13 19 R0 32 R0 40 R 46 R 42 RC 54.8 21. 55 21.55 635 400 16 R0 17 R 21 Re 39 RC 42 R 44 R 54. 5 21. 42 21. 42 635 400 19 RC 19 RC 22 Rc 31 R0 0 R0 40 R 55. 5 22.0 22. 0 635 400 84 RB 24 R 32 R0 39 RC 43 RC 44R 55.0 22.0 22.0 635 400 92 RB 24 RC 28 R 36 Re 40 RC 39 Re 54. 0 22. 0 22. 0 635 400 54. 5 22.0 22.0 635 400 18 RC 31 R0 38 RC 45 Re 47 Re 48 Re 54. 0 22. 0 22. 0 635 400 20 R 34 R0 38 R0 44 R 46 R 47 R 53.0 22.0 22.0 635 400 17 RC 26 RC R RC 43 R RC Time at temperature=40 minutes.

cent manganese and from about 0.3 to about 0.7 wt. percent silicon and/ or magnesium, with the remainder being copper.

In order to provide maximum hardness properties these novel alloys were subjected to the following two-step heat treatment:

Quenching medium= Room temperature water.

Table III shows the effect of cold rolling, between solution and aging heat treatments, upon the maximum attainable hardness of the same alloys as set forth in Table 11. Here again, the 0.5% Si or 0.5 Mg or the Si plus Mg combinations showed up best and the final hardnesses were up to 5 points R higher than the same alloys when not cold rolled.

TABLE III.PRECIPITATION HARDENING DATA FOR COLD ROLLED NOMINAL 22% Ni, 22% Mn, Cu ALLOYS WITH Si, Mg, AND SH-Mg ADDED OF TABLE II Nominal Solution Percent Cold Hardness Total aging time, hours (Aging temp.=400 O.) No charge treatment Initial Final reduction, after cold composition temperature, thickness thickness T0TF/T rolling See Table 0. LB 0. 098 49. 3O G35 Cracked severely during hot rolling 635 0.193 0.151 21.78 23 R 35 R 41 RC 41 R 48 R0 49 R 50 03s 0. 192 0. 147 48 635 0. 205 0. 190 47 Time at temperature=40 minutes.

Step 1.S0luti0n treatment In this step the alloys are heated at a temperature of between 575 C. and 800 C. until they are heated through and the second phase or phases is adequately in solid solution and then rapidly cooled to room temperature. The rapid cooling may be accomplished by quenching in room temperature water. In order to avoid excessive grain growth and surface oxidation, a lower solution treating temperature is used whenever possible.

Step 2.Aging treatment The aging or hardening treatment may be performed at any temperature within the range of from 400-500 C. The time to reach the maximum hardness and the maximum hardness attained are dependent mainly upon the Quenching modium=ro0m temperature water.

Upon obtaining the data shown in Tables II and III above, the silicon and magnesium concentrations were maintained constantly at about 0.5 percent while the nickel and manganese contents were each varied from 1830 weight percent. Table IV shows these results and also shows that, for the most part, little advantage in maximum hardness is gained by raising nickel and manganese contents above about 25 weight percent of each. In addition, alloys 16 and 17, with higher Ni and Mn concentrations, fractured during hot rolling. As a result of this data it appears that for the low additions of Si or Mg, that is about 0.5% of each, the most compatible Ni and Mn content is in the range of 19 to 25 weight percent of each. Increase in the content of Ni and Mn,

while increasing the hardness only slightly, causes alloy fabrication problems and embrittles the final product.

6 Alloys 16A and 17A from Table V were then subjected to an accumulation of heating at 500- and 550 C.

TABLE IV.PRECIPITATION HARDENING DATA FOR HOT ROLLED OR CAST ALLOYS OF VARIABLE Ni-AND Mn PLUS 0.5% Si OR 0.5% Mg Nominal charge composition Solution Total aging time, hours (Wt. percent) As rolled treatment Solution Aging No. hardness temperatreatment temperature, C.* hardness ture, "0. Cu Ni M11 Si Mg 2 5 30 60 90 39.5 30. 30. 400 28 Re 34 Re 38 R0 43 R 46 R0 46 R 45.5 27. 27. 400 24 Re 36 RC 38 Re 44 Re 46 Re 47 R 51.5 24. 24. 400 14 R 30 Rc 35 R0 39 R0 45 B 45 Be 57.5 21. 21. 400 9 R0 23 R0 32 R 39 R 42 R 42 RC 63.5 18.0 18. 400 84 RB 11 RC 22 R0 35 R0 39 Re 41 Be 38.8 30.7 29.5 400 R 32 R 35 R 44 R 45 R 48 Rs 45.5 27.0 27.0 400 4 R0 21 R 29 R0 35 RC 41 Re 43 R 51.5 24.0 24.0 400 12 Re 27 Re 32 R0 38 R0 39 R0 42 Rs 57.5 21.0 21.0 400 80 RB 19 R0 31 R0 36 R0 38 Re 41 R0 (53.5 18.0 18.0 400 71 RB 12 R0 20 Re 33 R0 37 Re 38 R0 *Time at temperature=40 minutes.

From the above data it is seen that the addition of 20 to determine the influence on hardness and toughness of small quantities of silicon and/ or magnesium to the Type 720 alloy, which normally has a maximum hardness which is too low for many tool applications, results in the alloy having exceptional hardness values. Addition of the Si and/or Mg in small quantities to the Type 730 alloy enables the lowering of the Ni and Mn concentrations which thereby increases the toughness and lowers TABLE VI.DATA ON OVERAGING (TO IMPROVE TOUGI-INESS) OF TWO Cu-NiMn-0.5 Mg ALLOYS the brittleness of the composition. Moreover, by the lowering of the Ni and Mn concentrations, these strategic materals may be used for other purposes.

Table V below shows that by cold rolling the alloys of Table IV, between solution treatment and aging, several changes occur:

(1) The alloys reach maximum hardness in a shorter time period.

(2) Final hardness obtained is as much as 10 points R higher than the same alloys not rolled.

(3) The hardening benefits obtained by the higher Ni and Mn contents are further minimized, the hardness spread being only about 6 points R between a 20% Ni, 20% Mn-X-Cu alloy and a Ni-30%MnX-Cu alloy, where X may be either 0.5% silicon or 0.5% magnesium.

(4) The higher Ni and Mn alloys with magnesium added, while quite hot short or difiicult to roll hot, cold rolled easily at room temperature following the solution treatment.

In addition to the findings summarized above, these new alloy combinations containing Cu-NiMn, with additions of silicon, magnesium and silicon/magnesium, have been found to possess a maximum permeability of less than 1.02 regardless of the state of fabrication or point in the heat treating schedule.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent of the United States is:

1. A hardenable, non-magnetic alloy consisting essentially of nickel, manganese, silicon and copper, said nickel being present in an amount from about 19-25 weight percent, said manganese in an amount from about 19-25 weight percent, said silicon in an amount up to about 1.5 weight percent, the remainder being copper.

TABLE V.-PRECIPITATION HARDENING DATA FOR COLD ROLLED ALLOYS OF VARIABLE Ni AND Mn PLUS 0.5% Si OR 0.5% Mg OF TABLE IV Nominal Solution Pereent Cold Hardness Total aging time, hours (Aging t-einp.=400 C.) No. charge treatment Initial Final reduction, after cold composition temperature, thickness thickness TuT /TO rolling 635 .202 .125 38.1 26 Re 43 R0 47 Re 50 Re 52 Re 52 Re 54 Re 635 199 124 37. 7 635 200 114 43.0 635 197 .104 47. 2 See Table 635 201 113 43.8 IV. 635 .230 .097 2 57. 8 635 .232 .081 7 65. 1 635 .195 .070 61. 0 635 .195 .077 60.5 47 R 4 RC 49 RC 35 1378 2601] 20 C a 27 R0 29 R0 36 R0 41 R0 44 Re 44 R 1 Time at temperature=40 minutes.

2 The alloys with magnesium additions, particularly alloys 16 and 17, had a tendency to be hot short when rolled hot. Specimens 16 and17 were incapable of any hot rolling at the temperature used. Alloys 18 and 19 edge cracked badly during hot rolling. H

owever, all of these alloys, after solution treatment, cold rolled at room temperature more readily than the alloys with silicon additions (Alloys 10 to 15).

2. The alloy of claim 1 wherein the silicon is present in an amount from about 0.3 to 0.7 Weight percent.

3. A handenable, non-magnetic alloy consisting essentially of nickel, manganese, magnesium and copper, said nickel being present in an amount from about 1925 Weight percent, said manganese in an amount from about 19-25 weight percent, said magnesium in an amount up to about 1.0 weight percent, the remainder being copper.

4. The alloy of claim 3 wherein the magnesium is present in an amount from about 0.3 to 0.7 weight percent.

5. A hardenable, non-magnetic alloy consisting essentially of nickel, manganese, a mixture of magnesium and silicon, and copper, said nickel being present in an amount from about 1925 weight percent, said manganese from about 19-25 weight percent, said mixture of magnesium and silicon in an amount up to about 2.0 weight percent, the remainder being copper.

' 6. The alloy of claim 5 wherein the mixture of silicon and magnesium is present in an amount from about 0.3 to 0.7 weight percent.

References Cited by the Examiner UNITED STATES PATENTS 2,157,934 5/1939 Hensel et al. 14832.5 2,224,573 12/1940 Hunter 75-159 XR 2,234,552 3/1941 Dean et al. l4832 2,275,188 3/1942. Harrington 148-160 XR 2,430,306 11/1947 Smith 75-159 3,072,508 1/1963 Klement et al. 148160 FOREIGN PATENTS 497,166 10/1953 Canada.

DAVID L. RECK, Primary Examiner. 

1. A HARDENABLE, NON-MAGNETIC ALLOY CONSISTING ESSENTIALLY OF NICKEL, MANGANESE, SILICON AND COPPER, SAID NICKEL BEING PRESENT IN AN AMOUNT FROM ABOUT 19-25 WEIGHT PERCENT, SAID MANGANESE IN AN AMOUNT FROM ABOUT 19-25 WEIGHT PERCENT, SAID SILICON IN AN AMOUNT UP TO ABOUT 1.5 WEIGHT PERCENT, THE REMAINDER BEING COPPER. 